The present disclosure relates to diffusers, and more specifically to nanoparticle diffusers. In optics, diffusers are materials or devices that diffuse or scatter light. Diffusers cause light to spread evenly across a surface, minimizing or removing high intensity bright spots. Diffusers can be used as screens or targets in imaging applications, in sensors, in cameras, or as calibration standards.
Lambertian diffusers are ideal diffusers having an ideal “matte” or diffusely reflecting surface. To an observer, the apparent brightness of an ideal Lambertian surface is the same regardless of the observer's viewing angle. Lambertian diffusers are used as reflectance standards on space sensors, such as Visible Infrared Imaging Radiometer Suites (VIIRS). Lambertian diffusers are also used as instrument components in space, airborne, tactical, and commercial applications.
Sintered polytetrafluoroethylene (PTFE) (commercially available as SPECTRALON® from Labsphere, Inc., North Sutton, N.H.) is a high reflectance Lambertian diffuser. The reflectance from sintered PTFE diffusers arises from the material's surface and subsurface structure. The porous thermoplastic particle network produces multiple reflections inside the material. The material should be kept free from contaminants to maintain its reflectance properties. However, the open hydrophobic structure of sintered PTFE readily absorbs impurities and contaminants, such as non-polar solvents, greases and oils. Sintered PTFE is also a soft material that is easily scratched and can require extreme care in handling and cleaning. Because it is easily contaminated with organics, sintered PTFE yellows upon exposure to ultraviolet (UV) light when contaminated.
Ground glass that is another example of a diffuser. The surface of ground glass has been mechanically ground and processed to produce a flat but rough, or matte, finish. However, ground glass produces lower signal levels. Ground glass also does not produce a sufficiently optically flat scattered light distribution necessary for many applications.